10 Ways Dark Matter Could Explain The Universe
By Heather Ramsey,
Listverse, 18 March 2015.

Dark matter particles don’t produce, reflect, or absorb light. However, even though we can’t see dark matter directly and we still don’t understand its nature, scientists believe it makes up about 26 percent of our known universe, based on how its gravitational pull interacts with other space objects. Like wind blowing the branches of a tree, we can’t see dark matter but we can see how it affects its surroundings. From these observations and analysis, our scientists are developing fascinating theories about dark matter. If true, they may change our understanding of the universe in profound ways.

10. Dark Matter May Cause Mass Extinctions

Photo credit: NASA

Michael Rampino, a biology professor from New York University, believes that Earth’s movement through the galactic disk (our region in the Milky Way galaxy) may have caused mass extinction events on Earth. This happened because our movement disturbed the orbit of comets in the outer solar system (known as the “Oort Cloud”) and increased the heat in our planet’s core.

With its planets in tow, the Sun orbits the centre of the Milky Way every 250 million years. During its journey, it weaves through the galactic disk about every 30 million years. Rampino argues that Earth’s trek through the disk coincides with comet impacts and mass extinction events on Earth, including the one 65 million years ago when an asteroid is believed to have killed the dinosaurs. There’s also a theory that volcanic eruptions were thinning the dinosaur herd right before an asteroid finished them off.

The combination of unusual volcanic activity and an asteroid strike coinciding with Earth’s orbit through the galactic disk would play into Rampino’s theory perfectly. “While traveling through the disc, the dark matter concentrated there disturbs the pathways of comets typically orbiting far from the Earth in the outer solar system,” Rampino said. “This means that comets that would normally travel at great distances from the Earth instead take unusual paths, causing some of them to collide with the planet.” Some argue that Rampino’s theory doesn’t work because the dinosaurs died by an asteroid, not a comet. However, approximately 4 percent of the Oort Cloud is made up of asteroids, which equates to eight billion of them floating around out there.

In addition, Rampino believes that each of Earth’s orbits through the galactic disk causes dark matter to accumulate in the planet’s core. As the particles of dark matter annihilate each other, they create intense heat that may cause volcanic eruptions, sea level changes, mountain building, and other geological activity that also dramatically affects biological life on Earth.

9. The Milky Way May Be A Huge Wormhole

Photo credit: Alain r/Wikimedia

Is it possible that we’re living in a giant tunnel that provides a shortcut through the universe?

As predicted by Einstein’s general theory of relativity, a wormhole is a region where space and time bend to create a shortcut to a distant part of the universe. According to astrophysicists from the International School for Advanced Studies in Trieste, Italy, dark matter in our galaxy could be distributed in a way that permits a stable wormhole to exist in the middle of our Milky Way. These scientists believe that it may be time for us to rethink the nature of dark matter. Maybe dark matter is simply another dimension.

“If we combine the map of the dark matter in the Milky Way with the most recent big bang model to explain the universe,” said Professor Paulo Salucci, “and we hypothesize the existence of space-time tunnels, what we get is that our galaxy could really contain one of these tunnels, and that the tunnel could even be the size of the galaxy itself. But there’s more. We could even travel through this tunnel, since, based on our calculations, it could be navigable. Just like the one we’ve all seen in the recent film Interstellar.”

Of course, it’s just a theory. But scientists believe that dark matter could be the key to creating wormholes and determining how to observe them. So far, no natural wormholes have been discovered.

8. The Discovery Of Galaxy X


Galaxy X is also known as the dark matter galaxy, a mostly unseen dwarf galaxy that may be causing odd ripples in the cold hydrogen gas at the outer limits of the Milky Way’s disk. Believed to be a satellite galaxy of the Milky Way, Galaxy X houses a cluster of four Cepheid variables, pulsating stars used as markers to help us measure distances in space. We can’t see the rest of this dwarf galaxy because it’s supposedly made up of invisible dark matter. However, the immense gravitational pull of that dark matter galaxy probably caused the ripples we have seen. Without a gravitational source like dark matter keeping them together, it’s also highly unlikely that four Cepheid variable stars would be positioned so close to one another in the middle of space rather than flying apart.

“The discovery of the Cepheid variables shows that our method of finding the location of dark-matter dominated dwarf galaxies works,” said astronomer Sukanya Chakrabarti. “It may help us ultimately understand what dark matter is made up of. It also shows that Newton’s theory of gravity can be used out to the farthest reaches of a galaxy and that there is no need to modify our theory of gravity.”

7. Disintegration Of The Higgs Boson Into Dark Matter

Photo credit: CERN

Developed in the 1970s, the Standard Model of particle physics is a set of theories that supposedly predicts all the known subatomic particles in the universe and how they interact. With the 2012 confirmation of the existence of the Higgs boson (also known as the “God particle”), the Standard Model was complete. Unfortunately, that model doesn’t explain everything, especially dark matter, the gravitational force that holds galaxies together. The mass of the Higgs particle also seems much too low to some scientists.

That propelled researchers at Chalmers University of Technology to propose a new model based on super symmetry, which gives every known particle in the Standard Model a heavier super partner. According to this new theory, a small proportion of Higgs particles will decay into a photon (a light particle) and two gravitinos (dark matter particles). “If the model is found to fit, it would completely change our understanding of the fundamental building blocks of nature,” said Christoffer Petersson of Chalmers. The model will be tested at the Large Hadron Collider in Switzerland.

6. Dark Matter In The Sun

Photo credit: NASA

Depending on the method used to analyze the Sun, the amount of elements heavier than hydrogen or helium fluctuates by 20–30 percent. We can measure each of those elements by looking at the spectrum of light it emits, like a distinct fingerprint, or by studying how it affects sound waves traveling through the Sun, which then cause small changes in the Sun’s brightness. The mysterious difference between these two measurements of the Sun’s elements is called the solar abundance problem.

We need accurate measurements of these elements to understand the chemical composition of the Sun as well as its density and temperature. In many ways, it will also help us to understand the makeup and behaviour of other stars as well as their planets and galaxies.

For years, scientists have been unable to devise a workable solution. Then astroparticle physicist Aaron Vincent and his associates suggested dark matter in the Sun’s core as a possible answer to the problem. After running many simulations, they came up with a theory that seemed to work. However, it included a special type of dark matter, called “weakly interacting asymmetric dark matter,” which can be either matter or antimatter but not both.

From measurements of gravity, scientists know that a halo of dark matter surrounds the Sun. Asymmetric dark matter particles don’t contain much antimatter, so they can survive contact with normal matter and build up in the Sun’s core. These particles are also believed to absorb energy in the centre of the Sun and then transport that heat to the outer edges, which could account for the solar abundance problem.

“The main advantage of asymmetric dark matter is that a lot of it can accumulate in the Sun as it speeds through the dark-matter cloud that engulfs the Milky Way,” Vincent said. “If the dark matter was self-annihilating, the dark matter would disappear before transporting any sizable amount of heat from the Sun’s core.”

5. Dark Matter May Be Macroscopic


Researchers at Case Western Reserve have questioned whether scientists are looking for dark matter in the right places. Specifically, they’re suggesting that dark matter may not be made of tiny exotic particles like WIMPs (weakly interacting massive particles) but instead of macroscopic objects that may range from a couple of ounces to as large as an asteroid. However, these scientists are limiting their theory of where to look by taking into account what has already been observed in space. This leads them to believe that the Standard Model of particle physics will provide the answer. They don’t believe a new model is necessary for dark matter.

The researchers have dubbed their dark matter objects “macros.” They’re not suggesting that we eliminate WIMPS and axions (weakly interacting low-mass particles) from consideration but simply that we broaden the search for dark matter to include other candidates. There are examples of matter that are neither ordinary nor exotic, which haven’t been examined but that do fall within the parameters of the Standard Model.

“The community had kind of turned away from the idea that dark matter could be made of normal-ish stuff in the late ’80s,” said physics professor Glenn Starkman. “We ask, was that completely correct, and how do we know dark matter isn’t more ordinary stuff - stuff that could be made from quarks and electrons?”

4. GPS Detection Of Dark Matter


Two physicists have proposed using GPS satellites to find dark matter, which the scientists suggest may not be particles as commonly assumed but instead tears in the fabric of space-time. “Our research pursues the idea that dark matter may be organized as a large gas-like collection of topological defects, or energy cracks,” said Andrei Derevianko of the University of Nevada. “We propose to detect the defects, the dark matter, as they sweep through us with a network of sensitive atomic clocks. The idea is, where the clocks go out of synchronization, we would know that dark matter, the topological defect, has passed by. In fact, we envision using the GPS constellation as the largest human-built dark-matter detector.”

The researchers are analyzing data from 30 GPS satellites to see if their theory makes sense. If dark matter is indeed like a gas, Earth will pass through it while orbiting the galaxy. Acting like wind, clumps of dark matter will blow by Earth and its satellites, causing the GPS clocks in the satellites and on the ground to lose their synchronization on occasion for approximately three minutes. Scientists should be able to monitor any discrepancy over one-billionth of a second.

3. Dark Energy May Be Eating Dark Matter

Photo credit: NASA/ESA

According to recent research, dark energy appears to be eating dark matter as the two interact, which in turn slows the growth of galaxies and may ultimately make the universe almost an empty place. It could be that dark matter is decaying into dark energy, but we don’t know yet. The European Union’s Planck spacecraft recently gave us precise numbers on the physical makeup of the universe: 4.9 percent ordinary matter (which includes us), 25.9 percent dark matter, and 69.2 percent dark energy.

We can’t see dark matter or dark energy. Neither term is well understood even in the scientific community. They’re more like placeholder terms, describing something we believe is happening but can’t explain yet. So until we actually know what we’re talking about, we use these ambiguous terms.

Dark matter attracts, and dark energy repels. Dark matter is the backbone or framework upon which galaxies and their contents are built. Its gravitational pull is believed to hold the stars together in galaxies, for example. Gravity is stronger when objects are closer to each other and weaker when they’re farther apart.

On the other hand, dark energy describes the force that causes the universe to expand by propelling distant galaxies away from us. So as dark energy repels these objects, gravity weakens in space. This suggests that the expansion of space is accelerating, not slowing from the effects of gravity as once believed.

“Since the late 1990s, astronomers have been convinced that something is causing the expansion of our universe to accelerate,” said Professor David Wands of the University of Portsmouth. “The simplest explanation was that empty space - the vacuum - had an energy density that was a cosmological constant. However, there is growing evidence that this simple model cannot explain the full range of astronomical data researchers now have access to; in particular the growth of cosmic structure, galaxies, and clusters of galaxies, seems to be slower than expected.”

This energy transfer is only occurring on the dark side. Ordinary matter (like us) is not being swallowed by dark energy.

2. Dark Matter May Have Caused Ripples In The Galactic Disk


Looking out into space from Earth, we see the stars suddenly end about 50,000 light-years from the centre of our galaxy. So we figured that was the end of our galaxy. We didn’t see anything else significant until about 15,000 light-years beyond that edge, which was the Monoceros Ring of stars that extends above our galactic plane. Some of our scientists thought they were stars torn away from another galaxy.

However, a new analysis of data from the Sloan Digital Sky Survey reveals that the Monoceros Ring is actually part of our galaxy. That means the Milky Way is at least 50 percent larger than we thought - increasing our galaxy’s diameter from about 100,000–120,000 light-years to about 150,000–180,000 light-years.

Looking from Earth, we can’t see how it connects because of ripples in the galactic disk. It’s like watching waves in the ocean from the beach. As a wave rises up, it blocks your view of the ocean beyond, except for portions of even higher waves. So, even though our view was partially blocked by the shape of our galaxy, we saw the Monoceros Ring because it was like looking at the top of a higher wave.

This discovery changes our understanding of how the Milky Way is constructed. “In essence, what we found is that the disk of the Milky Way isn’t just a disk of stars in a flat plane - it’s corrugated,” said Heidi Newberg of the Rensselaer School of Science. “As it radiates outward from the Sun, we see at least four ripples in the disk of the Milky Way. While we can only look at part of the galaxy with this data, we assume that this pattern is going to be found throughout the disk.”

Like the ripples caused by a pebble thrown into a pond, scientists believe these ripples in our galaxy may have been caused by a lump of dark matter or a dwarf galaxy slicing through the Milky Way’s disk. If that theory is true, these ripples would give researchers a way to analyze the distribution of dark matter in the Milky Way.

1. The Gamma Ray Signature


Until recently, the only way scientists could detect dark matter was through observing its possible gravitational effect on other space objects. However, researchers believe that gamma rays may be a more direct signal that invisible dark matter lurks in our universe. In an exciting development, they may have just found that first gamma ray signature in Reticulum 2, a newly discovered dwarf galaxy near the Milky Way.

Gamma rays are a form of high-energy electromagnetic radiation emitted from the dense centres of galaxies. If it’s true that dark matter is made up of WIMPs, then dark matter particles would be a source of gamma rays produced when WIMPs annihilate one another on contact. However, gamma rays can also be emitted by other sources such as black holes and pulsars. If our analysis can eliminate these other sources of gamma rays, then it’s possible that any remaining gamma rays may be coming from dark matter. At least, that’s the theory.

Scientists believe that most dwarf galaxies lack significant sources of gamma rays other than dark matter, which may comprise as much as 99 percent of a dwarf galaxy. That’s why physicists from Carnegie Mellon, Brown, and Cambridge universities became excited by the discovery of gamma rays emanating from Reticulum 2.

“The gravitational detection of dark matter tells you very little about the particle behaviour of the dark matter,” said Matthew Walker of Carnegie Mellon University. “But now we may have a non-gravitational detection that shows dark matter behaving like a particle, which is a holy grail of sorts.” Of course, it’s possible there are other sources of gamma rays in dwarf galaxies that we haven’t identified yet. However, the recent discovery of nine potential dwarf galaxies near the Milky Way may give scientists the opportunity to further explore this theory of detecting dark matter.

Top image: A three-dimensional map offering a first look at the web-like large-scale distribution of dark matter, an invisible form of matter that accounts for most of the Universe's imaginary mass. Credit: NASA/ESA/Richard Massey (California Institute of Technology)/Wikimedia Commons.

[Source: Listverse. Edited. Top image added.]

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